The present invention relates to subterranean treatment fluids, and more particularly, the present invention relates to subterranean treatment fluids comprising relative permeability modifiers and methods for using such subterranean treatment fluids in subterranean operations to reduce the production of water from and stimulate hydrocarbon production in a subterranean formation.
The production of water with hydrocarbons from subterranean wells constitutes a major problem and expense in the production of the hydrocarbons. While hydrocarbon-producing wells are usually completed in hydrocarbon-bearing formations, such formations may contain, or may be adjacent to, water-bearing sections. Generally, the term “water-bearing section” refers to any portion of a subterranean formation that may produce water, including a hydrocarbon-bearing section that has sufficiently high water saturation such that water may be produced along with hydrocarbons. The high mobility of the water may allow it to flow into the well bore by way of natural fractures and/or high permeability streaks present in the formation. Over the life of such wells, the ratio of water to hydrocarbons recovered may be undesirable in view of the cost of producing the water, separating it from the hydrocarbons, and disposing of it, which can represent a significant economic loss.
Subterranean stimulation treatments have long been used in the field of hydrocarbon production to increase the flow of hydrocarbons to the well bore. One such stimulation treatment is hydraulic fracturing, where specialized fluids are pumped into the subterranean formation at sufficient pressures to create or enhance at least one fracture within the formation, thereby increasing fluid flow through the formation to the well bore. When a formation contains water-bearing sections, however, stimulation may lead to the undesired, increased production of water with the hydrocarbons.
Another subterranean stimulation treatment is acid stimulation (e.g., “acidizing”), in which an aqueous treatment fluid comprising an acid is introduced into the formation to dissolve acid-soluble materials that may clog or constrict formation channels, thereby potentially widening the pathways through which hydrocarbons may flow from the formation into the well bore. Acid stimulation treatments also may facilitate the flow of injected treatment fluids from the well bore into the formation. One method of acidizing, known as “fracture acidizing,” usually comprises injecting an acidizing treatment fluid into the subterranean formation at a pressure sufficient to create or enhance at least one fracture within the formation. Another method of acidizing, known as “matrix acidizing,” usually comprises injecting the acidizing treatment fluid into the formation at a pressure below that which would create or enhance at least one fracture within the subterranean formation. In certain circumstances, however, the acidizing treatment fluids may undesirably enter the water-bearing sections instead of the hydrocarbon-bearing sections in the formation because the water-bearing sections may be more permeable to the aqueous acidizing treatment fluid than the hydrocarbon-bearing sections. Thus, acid stimulation treatments may result in an undesirable increase in the production of water.
A variety of techniques have been used to reduce the production of undesired water and/or to divert the aqueous acidizing treatment fluid away from the water-bearing sections and into the hydrocarbon-bearing sections. One attempt has involved the injection of particulates, foams, or blocking polymers into the subterranean formation so as to plug off the water-bearing sections. Thus, the undesired production of water may be reduced, and, when used in an acid stimulation treatment, the acidizing treatment fluid may be diverted to the hydrocarbon-bearing sections rather than the water-bearing sections.
However, the use of these water-blocking techniques has proved to be problematic. For example, plugging off the water-bearing sections may not be suitable for treating a producing formation unless the injected solution (or material) can be injected solely into the offending water-bearing sections therein. Further, if a polymer solution is allowed to form a cross-linked polymer gel within a hydrocarbon-producing zone, the gel may reduce or stop the flow of hydrocarbons in addition to the flow of water. Even when a polymer solution is properly injected into a water-producing section, the cross-linked polymer gel formed therein may become unstable in the zone, due to factors such as thermal degradation, differences in the adsorption characteristics of the polymer and associated cross-linker, and the like. Furthermore, techniques geared toward injecting solutions (or materials) designed to plug off the water-bearing sections are limited because they may require expensive zonal isolation. Zonal isolation also may be inaccurate, which may lead to inadvertently plugging and/or damaging the hydrocarbon-bearing sections.
Recently, polymers referred to as relative permeability modifiers have been used, in some instances, to decrease the production of water with hydrocarbons. For example, relative permeability modifiers, such as polyacrylamide, have been introduced into hydrocarbon and water-producing formations so that the polymers may attach to adsorption sites on surfaces within the formations. Among other things, these relative permeability modifiers may reduce the flow of water through the formation. The use of relative permeability modifiers in hydrocarbon and water-producing formations to decrease the production of water involves less risk than other techniques and has the advantage of not requiring expensive zonal isolation techniques. However, the use of such relative permeability modifiers, e.g., polyacrylamides, has heretofore resulted in only small, temporary reductions in water production and/or unacceptable levels of reduction in hydrocarbon production.